I use the acrylic alot during the painting projects. I like it because I like water based products for ease in clean up. I have never use the oil, so I cannot get into this discussion.
On the power washing, be care ful with this type of siding, you can do more damage than good if your not careful. Never aim up the siding, this gets into the walls. go down. then use a fan tip, and use around 2200 psi's and stay about 12 inches from the work area.
do not paint for a good 3 days after power washing.
I would forgoe the power washing and do spot sanding and wire brushing and some spot replacement. The first coat will soak up very fast and your coverage per can will go down drastically.